Provide a callback that is fired after the InterProcessMutex creates its ephemeral node

InterProcessMutex performs two significant steps to acquire its lock:

1. Creates an ephemeral sequential node. This practically means that it took a position in the lock queue (i.e. based on its sequence value).
2. Blocks until the lock is acquired.

This improvement is about providing a callback that notifies the caller that the lock order is reserved.

The use for this, at least for us, is that we needed to differentiate between the two phases for higher concurrency because we can do other actions after knowing that the InterProcessMutex order is known. Especially since the lock acquisition can take too long, depending on the situation of course.